1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
In general, an image forming apparatus using an electrophotographic method employs charged toner having a polarity to form a toner image on a surface of a photoreceptor, and transfers the toner image to an intermediate transfer belt as a primary transfer. Subsequently, the toner image on the intermediate transfer belt is secondarily transferred to a recording medium, where a fixing process fixes the image on the medium to form a final image. The intermediate transfer belt and a transfer roller form a secondary transfer nip in between. In performing the secondary transfer, by applying a transfer voltage having an opposite polarity to the charged polarity of the toner on the intermediate transfer belt to the transfer roller, a transfer electrical field is formed at the secondary transfer nip that transfers the toner image on the intermediate transfer belt en bloc to the recording medium.
As illustrated in FIG. 19, in the transfer device, in the vicinity of the transfer electrical field before the transfer process performed at the secondary transfer nip N formed by the intermediate transfer belt 100 and the transfer roller 200, a space M (i.e., an electrical discharge area) exists between the intermediate transfer belt 100 and a recording sheet P. In the space M, part of toner on the intermediate transfer belt 100 disperses due to discharging generated by the electrical field and the dispersed part of toner attaches to the recording sheet P, thereby causing the image on the recording sheet P to be disturbed. To prevent this, as illustrated in FIG. 20, a roller 300 is additionally disposed before the secondary transfer nip N to cause the intermediate transfer belt 100 and the recording sheet P to be closely attached to each other before the space M, thereby minimizing the effect of the electrical discharge. However, disposition of the roller 300 to change a route of the intermediate transfer belt 100 may cause a cost rise, and increase in the thickness of the transfer device due to the enlarged mounting space, which may cause the transfer device to be larger.
As another method to prevent the effect of the electrical discharge, for example, it is known that the provision of a guide before the transfer nip enables the recording medium P to closely attach to the intermediate transfer belt before the secondary transfer nip N. JP-2006-301509-A, JP-2008-026533-A, and JP-4038328-B disclose an image forming apparatus using this type of guide before the transfer nip. In addition, JP-4038328-B discloses provision of two guide members so as to keep a close contact between the image carrier and the transfer member, which increases the size of the apparatus.
Yet the conventional guide member before transfer has various problems such as distortion of the guide member due to interference with the transfer belt or other parts or components.